diff --git a/packages/react-native/ReactCommon/react/performance/timeline/tests/PerformanceEntryCircularBufferTest.cpp b/packages/react-native/ReactCommon/react/performance/timeline/tests/PerformanceEntryCircularBufferTest.cpp
new file mode 100644
index 000000000000..de0d8e29702d
--- /dev/null
+++ b/packages/react-native/ReactCommon/react/performance/timeline/tests/PerformanceEntryCircularBufferTest.cpp
@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+
+#include <string>
+#include <variant>
+#include <vector>
+
+#include "../PerformanceEntry.h"
+#include "../PerformanceEntryCircularBuffer.h"
+
+namespace facebook::react {
+
+namespace {
+
+std::string getName(const PerformanceEntry& entry) {
+  return std::visit([](const auto& data) { return data.name; }, entry);
+}
+
+std::vector<std::string> getNames(
+    const std::vector<PerformanceEntry>& entries) {
+  std::vector<std::string> names;
+  names.reserve(entries.size());
+  for (const auto& entry : entries) {
+    names.push_back(getName(entry));
+  }
+  return names;
+}
+
+PerformanceEntry makeMark(const std::string& name) {
+  return PerformanceMark{{.name = name, .startTime = HighResTimeStamp::now()}};
+}
+
+} // namespace
+
+// Overflowing the buffer must overwrite the oldest entries and increment
+// droppedEntriesCount by exactly the number of evictions (not by the number of
+// adds beyond capacity at any other rate).
+TEST(PerformanceEntryCircularBufferTest, AddTracksDroppedEntriesOnOverflow) {
+  PerformanceEntryCircularBuffer buffer{3};
+
+  buffer.add(makeMark("a"));
+  buffer.add(makeMark("b"));
+  buffer.add(makeMark("c"));
+
+  // Filling up to capacity must not drop anything.
+  EXPECT_EQ(0u, buffer.droppedEntriesCount);
+
+  buffer.add(makeMark("d"));
+  buffer.add(makeMark("e"));
+
+  EXPECT_EQ(2u, buffer.droppedEntriesCount);
+
+  std::vector<PerformanceEntry> entries;
+  buffer.getEntries(entries);
+  EXPECT_EQ((std::vector<std::string>{"c", "d", "e"}), getNames(entries));
+}
+
+// getEntries(target) must append (not replace) the buffer contents to the
+// caller-provided target vector, preserving any pre-existing elements.
+TEST(PerformanceEntryCircularBufferTest, GetEntriesAppendsToTarget) {
+  PerformanceEntryCircularBuffer buffer{5};
+  buffer.add(makeMark("x"));
+  buffer.add(makeMark("y"));
+
+  std::vector<PerformanceEntry> target;
+  target.push_back(makeMark("preexisting"));
+
+  buffer.getEntries(target);
+
+  EXPECT_EQ(
+      (std::vector<std::string>{"preexisting", "x", "y"}), getNames(target));
+}
+
+// getEntries(target, name) must only return entries matching the given name,
+// even when entries of other variant types share the buffer.
+TEST(PerformanceEntryCircularBufferTest, GetEntriesByNameFiltersAcrossTypes) {
+  PerformanceEntryCircularBuffer buffer{10};
+  buffer.add(
+      PerformanceMark{{.name = "foo", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMeasure{
+          {.name = "bar", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMark{{.name = "foo", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceLongTaskTiming{
+          {.name = "foo", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMeasure{
+          {.name = "foo", .startTime = HighResTimeStamp::now()}});
+
+  std::vector<PerformanceEntry> matches;
+  buffer.getEntries(matches, "foo");
+
+  EXPECT_EQ(4u, matches.size());
+  for (const auto& entry : matches) {
+    EXPECT_EQ("foo", getName(entry));
+  }
+
+  std::vector<PerformanceEntry> noMatches;
+  buffer.getEntries(noMatches, "missing");
+  EXPECT_TRUE(noMatches.empty());
+}
+
+// clear() must empty the buffer so a subsequent getEntries returns nothing,
+// while leaving droppedEntriesCount untouched (it tracks lifetime overflow,
+// not current contents).
+TEST(
+    PerformanceEntryCircularBufferTest,
+    ClearEmptiesBufferButKeepsDroppedCount) {
+  PerformanceEntryCircularBuffer buffer{2};
+  buffer.add(makeMark("a"));
+  buffer.add(makeMark("b"));
+  buffer.add(makeMark("c")); // evicts "a"
+  ASSERT_EQ(1u, buffer.droppedEntriesCount);
+
+  buffer.clear();
+
+  std::vector<PerformanceEntry> entries;
+  buffer.getEntries(entries);
+  EXPECT_TRUE(entries.empty());
+  EXPECT_EQ(1u, buffer.droppedEntriesCount);
+
+  // The buffer remains usable after clear.
+  buffer.add(makeMark("d"));
+  buffer.getEntries(entries);
+  EXPECT_EQ((std::vector<std::string>{"d"}), getNames(entries));
+}
+
+// clear(name) must remove only entries whose name matches, regardless of
+// variant type, and leave other entries (and their order) intact.
+TEST(PerformanceEntryCircularBufferTest, ClearByNameRemovesOnlyMatching) {
+  PerformanceEntryCircularBuffer buffer{10};
+  buffer.add(
+      PerformanceMark{{.name = "keep", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMeasure{
+          {.name = "drop", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMark{{.name = "drop", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceLongTaskTiming{
+          {.name = "keep", .startTime = HighResTimeStamp::now()}});
+  buffer.add(
+      PerformanceMeasure{
+          {.name = "drop", .startTime = HighResTimeStamp::now()}});
+
+  buffer.clear("drop");
+
+  std::vector<PerformanceEntry> remaining;
+  buffer.getEntries(remaining);
+  EXPECT_EQ(2u, remaining.size());
+  for (const auto& entry : remaining) {
+    EXPECT_EQ("keep", getName(entry));
+  }
+
+  // Clearing a name that no longer exists is a no-op.
+  buffer.clear("drop");
+  remaining.clear();
+  buffer.getEntries(remaining);
+  EXPECT_EQ(2u, remaining.size());
+}
+
+} // namespace facebook::react